The proposed study examines the impact of an intensive weight loss program on untreated spouses and the home environment. Prior studies of weight control treatment have focused their assessments exclusively on the individual participant. This assessment strategy may underestimate the positive effects of weight control treatment and may miss important environmental predictors of weight loss outcomes. In the proposed study, 480 Look AHEAD participants and their spouses will be recruited from 3 clinical sites (Brown University, University of Alabama at Birmingham, University of Minnesota). Participants and spouses will be assessed at baseline and 1-year follow-up. Information on participants' weight, height, and demographics will be obtained from the Coordinating Center. In addition, participants will complete measures of dietary intake and physical activity (if not included in the core assessments) and social support. Spouses' weight and height will be measured and they will complete assessments of dietary intake and physical activity. Spouses will also be the primary reporter of the home environment and will complete measures of food availability, food storage, and amount of exercise equipment in the home. Our primary analysis will examine whether untreated spouses of intervention participants lose more weight than untreated spouses of standard care participants. Our secondary analyses will examine whether changes in participants' weight and weight-related behaviors from baseline to 1-year are correlated with changes on the same measures in spouses over the same time period. We will also examine whether more change is observed in the home environments of intervention participants than standard care participants and whether these changes predict participant and spouse weight loss. Finally, we will explore whether changes in the home environment mediate the relationship between participant and spouse weight loss. The data collected in the ancillary study will provide new information about the reach of behavioral weight loss treatment and about the role of the home environment in weight loss.